The present invention relates to activators having reduced volatility that are liquid at room temperature, which activators make it possible to produce polyurethane foams having improved emission behavior.
In the production of cellular or compact polyurethanes, organometallic compounds and tertiary amines are primarily used as catalysts. A disadvantage of tertiary amines is their volatility. Various methods for reducing the volatility of tertiary amines have been proposed. When higher molecular weight compounds are used, the price paid for lower volatility is lower activity, which must be compensated for by the addition of an increased amount of catalyst.
EP-A 176 013 teaches use of aminoalkylureas as activators. These compounds already have reduced volatility and cause less contact discoloration of covering and lining materials adjacent to the polyurethane. However, their production requires long reaction times and their emission behavior does not yet meet the high demands of the automotive industry.
DE-OS 30 27 796 describes dialkylaminoalkylureas as activators for the production of polyurethane foams. These activators are prepared by reaction of secondary amines with diisocyanates in organic solvents and are obtained, after concentration, in the form of highly viscous to crystalline products. They must then be converted into a form suitable for use in the production of polyurethanes, since they cannot readily be processed in the form of the pure product. Such a conversion is complex and expensive.
It has now been found that particular urea derivatives and urethane derivatives, which can be obtained by reaction of specific amines with higher-functional polyisocyanates and isocyanate-reactive compounds, possess excellent solubility properties and exhibit low volatility and high activity in polyurethane foam-forming systems. Use of these activators results in extremely low emissions, even when subjected to heat, and does not damage other materials adjacent to the polyurethane. These advantages are important in connection with the problem of fogging (i.e., emissions in the interior of a motor vehicle), especially under the effect of heat, which can impair adjacent materials and can be detected in the air inside the motor vehicle.
The present invention relates to an activator useful for the production of polyurethane foams and to a process for the production of polyurethane foams in which this activator is employed. The activator of the present invention is a reaction product of
A) a secondary amine or primary alcohol having at least one tertiary amino group,
B) a polyisocyanate of the diphenylmethane series having a functionality of from 2.5 to 4.0, preferably from 2.5 to 3.5, and
C) an OH-functional reactive component capable of addition to isocyanate, preferably having a number-average molecular weight of from 62 to 750.
The reaction is preferably carried out with stoichiometric amounts of isocyanate B) and the secondary amine or primary alcohol having at least one tertiary amino group A). That is, one amino group or hydroxyl group of the secondary amine or primary alcohol having at least one tertiary amino group A) is present in the reaction mixture for each NCO group of the isocyanate B). The activator-forming reaction is preferably carried out in a manner such that the solvent component C) and component A) are placed in a vessel and the isocyanate B) is added at a temperature of from 20 to 50xc2x0 C. When the addition of the isocyanate B) is complete, the reaction is carried out until no free NCO groups are present in the reaction mixture. This reaction is generally carried out at temperatures of from 20 to 100xc2x0 C., preferably at from 40 to 60xc2x0 C., most preferably at approximately 50xc2x0 C., because at these temperatures, the solvent C) reacts with the isocyanate B) to only a minor extent.
The polyurethane foams of the present invention are generally produced by reacting
a) a polyisocyanate or polyisocyanate prepolymer,
b) at least one component that is reactive towards isocyanate groups and has a functionality of from 2 to 6 and a number-average molecular weight of from 1000 to 15,000,
c) optionally, a chain-lengthening agent having a molecular weight of from 62 to 999,
d) an activator according to the present invention,
e) water,
f) optionally, liquid CO2 or an organic blowing agent,
g) optionally, a stabilizer, and
h) optionally, further additives.
In a preferred embodiment of the invention, the polyurethane is bonded to or manufactured with another material. For example, the polyurethane may be coated with a film or the polyurethane may be produced by applying foam-forming mixture to the back of a film or by spraying the back of a film with the polyurethane-forming mixture.
Other materials to which the polyurethane may be applied or with which the polyurethane may be manufactured preferably include PVC, ABS, mixtures of PVC, ABS, polyvinyl acetate, polyvinylbutyral, homo- or co-polymers based on vinyl chloride, styrene, butadiene, isoprene, chloroprene, dichlorobutadiene, ethylene, propene and acrylonitrile in the form of films, coatings and edgings of various colors, lacquers based on cellulose esters, polyester resins, epoxy resins, alkyd resins, as well as oil lacquers or lacquers of a combination of these components, and textiles based on cotton or leather. In a particularly preferred embodiment, polyolefins are used as the material with which the polyurethane is manufactured.
Suitable isocyanates useful for producing polyurethanes in accordance with the present invention include organic diisocyanates, polyisocyanates and polyisocyanate prepolymers. Suitable diisocyanates and polyisocyanates include aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates, such as those described in Justus Liebigs Annalen der Chemie Volume 562, page 75 (1949). Examples of such isocyanates are those represented by the formula
Q(NCO)n
in which
n represents an integer from 2 to 4, preferably 2, and
Q represents an aliphatic hydrocarbon radical having from 2 to 18 (preferably from 6 to 10) carbon atoms, a cycloaliphatic hydrocarbon radical having from 4 to 15 (preferably from 5 to 10) carbon atoms, an aromatic hydrocarbon radical having from 6 to 15 (preferably from 6 to 13) carbon atoms, or an araliphatic hydrocarbon radical having from 8 to 15 (preferably from 8 to 13) carbon atoms.
Polyisocyanates such as those described in DE-OS 28 32 253 are preferred. It is particularly preferred to use readily available polyisocyanates such as 2,4- and 2,6-toluene diisocyanate as well as any desired mixtures of those isomers (xe2x80x9cTDIxe2x80x9d), polyphenyl-polymethylene polyisocyanates, such as those prepared by aniline-formaldehyde condensation and subsequent phosgenation (xe2x80x9ccrude MDIxe2x80x9d), and polyisocyanates containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups or biuret groups (xe2x80x9cmodified polyisocyanatesxe2x80x9d), especially those modified polyisocyanates which are derived from 2,4- and/or 2,6-toluene diisocyanate or from 4,4xe2x80x2-and/or 2,4xe2x80x2-diphenylmethane diisocyanate. It is also possible to use prepolymers of these isocyanates and organic compounds having at least one hydroxyl group. Examples of suitable hydroxyl group-containing compound are polyols or polyesters having from one to four hydroxyl groups and number-average molecular weights of from 60 to 1400.
Polyisocyanates that are available under the name xe2x80x9cpolymeric diphenylmethane diisocyanatexe2x80x9d and have a functionality greater than 2.0, mixtures thereof with diphenylmethane diisocyanate or ternary mixtures of polymeric diphenylmethane diisocyanate, diphenylmethane diisocyanate and toluene diisocyanate, as well as prepolymers prepared from the mentioned isocyanates are most preferred.
The isocyanate-reactive component contains at least one component that is reactive towards isocyanate groups and generally has a functionality of from 2 to 6 and a number-average molecular weight of from 1000 to 15,000. Such a component may be, for example, a polyether polyol such as a poly(oxyalkylene) polyol or a polyester polyol or a combination thereof.
Poly(oxyalkylene) polyols that may be used in the practice of the present invention may be prepared, for example, by polyaddition of an alkylene oxide to a polyfunctional starter compound in the presence of a basic catalyst. Preferred starter compounds are molecules having from two to six hydroxyl groups per molecule, such as water, triethanolamine, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, glycerol, trimethylolpropane, pentaerythritol, and sorbitol. Other possible starter compounds are ammonia and compounds having at least one primary or secondary amino group, such as aliphatic amines (e.g., 1,2-diaminoethane), an oligomer of 1,2-diaminoethane (for example, diethylenetriamine, triethylenetetramine or pentaethylenehexamine), ethanolamine, diethanolamine, 1,3-diaminopropane, 1,3-diaminobutane, 1,4-diaminobutane, 1,2-diaminohexane, 1,3-diaminohexane, 1,4-diaminohexane, 1,5-diaminohexane, 1,6-diaminohexane, aromatic amines such as 1,2-diaminobenzene, 1,3-diaminobenzene, 1,4-diaminobenzene, 2,3-diaminotoluene, 2,4-diaminotoluene, 3,4-diaminotoluene, 2,5-diaminotoluene, 2,6-diaminotoluene, 2,2xe2x80x2-diaminodiphenylmethane, 2,4xe2x80x2-diaminodiphenylmethane, 4,4xe2x80x2-diaminodiphenylmethane, and aromatic amines that are obtained by acid-catalyzed condensation of aniline with formaldehyde. The starter compounds may be used alone or in a mixture.
Alkylene oxides that are preferably used for the preparation of the poly(oxyalkylene) polyols are oxirane, methyloxirane and ethyloxirane. They may be used alone or in a mixture. When used in a mixture, it is possible to react the alkylene oxides randomly or block-wise or both in succession. Further details may be found in Ullmanns Encyclopxc3xa4die der Industriellen Chemie, Volume A21, p. 670 f (1992).
A suitable poly(oxyalkylene) polyol may also be a dispersion of a graft polymerization product in a poly(oxyalkylene) polyol. That polymerization product may be prepared, for example, by radical in situ polymerization of acrylonitrile and/or styrene in a poly(oxyalkylene) polyol. (See, for example, U.S. Pat. No. 3,523,093.) Other suitable polymerization products are, for example, polyurea compounds, polyhydrazides, and polyurethanes containing tertiary amino groups. Suitable methods for the preparation of dispersions of such polymerization products are described, for example, in EP-A 11 752, U.S. Pat. No. 4,374,209 and DE-OS 32 31 497. The proportion of polymerization products in the dispersion is preferably from 1 to 50 wt. %.
It is also possible to use one or more polyester polyols having number-average molecular weights of from 1000 to 30,000 g/mol., preferably, from 1000 to 10,000 g/mol., most preferably, from 2000 to 6000 g/mol., produced from an aromatic and/or aliphatic dicarboxylic acid and a polyol having at least two hydroxyl groups to produce polyurethanes in accordance with the present invention. Examples of suitable dicarboxylic acids are phthalic acid, isophthalic acid, terephthalic acid, fumaric acid, maleic acid, azelaic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, malonic acid and succinic acid. The pure dicarboxylic acid as well as any desired mixtures thereof may be used. Instead of the free dicarboxylic acids, the corresponding dicarboxylic acid derivatives, such as, for example, dicarboxylic acid mono- or di-esters of alcohols having from one to four carbon atoms, may also be used. Such esters are formed, for example, in the recycling of polyester waste. It is also possible to use as the acid component dicarboxylic acid anhydrides, such as phthalic anhydride or maleic anhydride. Preferably used as the alcohol component for the esterification are: ethylene glycol, diethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, glycerol, trimethylolpropane, pentaerythritol, or a mixture thereof. It is also possible to use a polyester polyol of a lactone (for example, xcex5-caprolactone) or of a hydroxycarboxylic acid (for example, a xcfx89-hydroxycarboxylic acid).
The isocyanate-reactive component used to produce polyurethanes in accordance with the present invention may also include a polyether ester polyol, such as any of those obtainable, for example, by reaction of phthalic anhydride with diethylene glycol and subsequent reaction with oxirane.
Further examples of suitable polyols which may be present in the isocyanate-reactive component are polyfunctional alcohols or amines or amino alcohols or mixtures thereof as well as their propoxylated and/or ethoxylated secondary products, and polyester polyols that are obtained by esterification of polyfunctional alcohols with polyfunctional carboxylic acids. The isocyanate-reactive component preferably has a primary hydroxyl group content of at least 75%.
In addition to the isocyanate and isocyanate-reactive components, chain-lengthening agents or crosslinking agents having a molecular weight of from 62 to 999 g/mol. may optionally be included in the polyurethane-forming reaction mixture. Examples of suitable chain-lengthening and crosslinking agents include: glycerol, glycols, sorbitol, alkanolamines and the alkoxylation products thereof. It is possible to use both aromatic and aliphatic lengthening agents. In addition to hydroxy-functional chain-lengthening agents or crosslinking agents, amino-functional chain-lengthening agents or crosslinking agents may also be used.
In accordance with the present invention, an activator is included in the polyurethane-forming reaction mixture. Suitable activators are reaction products of
A) a secondary amine or primary alcohol having at least one tertiary amino group,
B) a polyisocyanate of the diphenylmethane series having a functionality of from 2.5 to 4.0, preferably from 2.5 to 3.5, and
C) as solvent, an OH-functional reactive component capable of addition to isocyanate.
Component A) is preferably a bis(dialkylaminoalkyl)-amine or an N-hydroxyalkyl bis(tert.-aminoalkyl) ether. Special preference is given to compounds of the general formula 
wherein X=
in which
n, m, p, q represent integers from 2 to 5, and may be identical or different, and
R1, R2, R3, R4, R5 each represents a C1-C5-alkyl group, preferably methyl.
The use of bis(3-(N,N-dimethylamino)propyl)amine or 2-hydroxy-ethyl-trimethyl-diaminodiethyl ether as component A) is particularly preferred.
Component B) is preferably a polyisocyanate of the diphenyl-methane series having a polynuclear proportion of at least 20%.
Component C) acts as solvent for the addition products formed by reaction of components A) and B). It is usually used in amounts such that the concentration of the addition products of A) and B) in component C) is from 20 to 60 wt. %.
Examples of compounds that may be used as component C) are dipropylene glycol, tripropylene glycol, triisopropanolamine, and addition products of propylene oxide and triethanolamine.
The activator is usually used in an amount of from 0.1 to 10 parts by weight, preferably from 1 to 5 parts by weight, based on 100 parts by weight of the total weight of the isocyanate-reactive component and any chain-lengthening or crosslinking agent employed.
Water is used as a chemical blowing agent in an amount of from 0.5 to 7.0 wt. %, preferably from 1.0 to 4.0 wt. %, based on the total weight of isocyanate-reactive component and any chain-lengthening or cross-linking agent employed.
The polyurethane-forming reaction mixture may additionally contain liquid CO2 or one or more organic blowing agents as physical blowing agents. Examples of suitable physical blowing agents include: hydro-carbons, such as cyclopentane, isopentane, and n-pentane; halogenated hydrocarbons, such as dichloromethane, dichloromonofluoromethane, difluoromethane, trifluoromethane, difluoroethane, 1,1,1,2-tetrafluoroethane, tetrafluoroethane (R 134 or R 134a), 1,1,1,4,4,4-hexafluorobutane (R 356), 1,1,1,3,3-pentafluoropropane (R 245fa), 1,1,1,3,3-pentafluorobutane (R 365mfc), chlorodifluoroethanes, 1,1-dichloro-2,2,2-trifluoroethane, 2,2-dichloro-2-fluoroethane, heptafluoropropane and sulfur hexafluoride. Mixtures of those blowing agents may also be used. Other suitable blowing agents are carboxylic acids, such as formic acid, acetic acid, oxalic acid, and chemical blowing agents that liberate gases in the course of the foaming process, such as, for example, azo compounds. Such blowing agents are preferably used in combination with water.
Stabilizers which are especially useful include polyether siloxanes, particularly, water-soluble polyether siloxanes. The structure of those compounds is generally such that a copolymer of ethylene oxide and propylene oxide is bonded to a polydimethylsiloxane radical. Such stabilizers are described, for example, in U.S. Pat. Nos. 2,834,748; 2,917,480 and 3,629,308. Of particular interest are polysiloxane-polyoxyalkylene copolymers such as those disclosed in DE-OS 25 58 523 that are branched a plurality of times via allophanate groups.
In the production of the polyurethane foams in accordance with the present invention, additional auxiliary substances and additives may optionally be added to the polyurethane-forming reaction mixture. Examples are flameproofing agents such as, for example, tricresyl phosphate, tris-(2-chloroethyl) phosphate, tris-(2-chloropropyl) phosphate, tris-(2,3-dibromopropyl) phosphate, tetrakis-(2-chloroethyl)ethylene diphosphate, dimethylmethane phosphonate, diethanolaminomethyl-phosphonic acid diethyl ester, as well as halogen-containing polyols having a flameproofing action. It is also possible to use paraffins or fatty alcohols or dimethylpolysiloxanes, pigments or coloring agents, stabilizers against the effects of ageing and weathering, plasticizers such as dioctyl phthalate, substances having a fungistatic and bacteriostatic action, as well as fillers such as barium sulfate, kieselguhr, carbon black or prepared chalk. These substances are usually added to the isocyanate-reactive component in amounts of from 0 to 10 parts by weight, preferably from 0 to 5 parts by weight.
Further examples of surface-active additives and foam stabilizers that may optionally be used, as well as cell regulators, retarding agents, stabilizers, flame-retardant substances, coloring agents and fillers, substances having a fungistatic and bacteriostatic action, and details regarding the use and the action of such additives, are described in G. Oertel (eds.): Kunststoff-Handbuch, Volume VII, Carl Hanser Verlag, 3rd edition, Munich 1993, p. 110-115.